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|Digital stacking of Tech Pan films and the photometry of faint galaxies.|
We describe the processing and co-addition of digitised scans of TechPan films, and discuss the scientific and photometric gains obtainedfrom use of co-added films. This work is based on SuperCOSMOS scans at10μm resolution of small regions of the Virgo cluster, which formpart of a large-scale survey for low surface brightness galaxies inVirgo. Use of co-added Tech Pan films allows the detection and surfacephotometry of such galaxies to very faint limits, and therefore providesan invaluable tool for a deeper sampling of the cluster galaxyluminosity function over large areas of sky. The calibration stepsnecessary before the films can be stacked are described in detail, aswell as the stacking process itself. Median-stacking is found to be moreeffective than averaging or simple adding of individual images, mainlydue to its ability in removing spurious features present on singlefilms. We also discuss several of the properties of stacked Tech Panfilms, such as background variations, the extent of galaxy profiles andthe detectability of small, faint galaxies.
|Studies of the Virgo Cluster. II - A catalog of 2096 galaxies in the Virgo Cluster area.|
The present catalog of 2096 galaxies within an area of about 140 sq degapproximately centered on the Virgo cluster should be an essentiallycomplete listing of all certain and possible cluster members,independent of morphological type. Cluster membership is essentiallydecided by galaxy morphology; for giants and the rare class of highsurface brightness dwarfs, membership rests on velocity data. While 1277of the catalog entries are considered members of the Virgo cluster, 574are possible members and 245 appear to be background Zwicky galaxies.Major-to-minor axis ratios are given for all galaxies brighter than B(T)= 18, as well as for many fainter ones.
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